November 11, 2011

Solar System Ejected A Giant Planet 600 Million Years Ago

According to a study published in The Astrophysical Journal Letters, our solar system may have ejected a giant planet from its orbit and spared the Earth.

Experts wrote that Jupiter had helped eject another giant planet from our solar system when it was about 600 million years old.

"We have all sorts of clues about the early evolution of the solar system," author Dr. David Nesvorny of the Southwest Research Institute said in a press release. "They come from the analysis of the trans-Neptunian population of small bodies known as the Kuiper Belt, and from the lunar cratering record."

He determined that giant planets were affected by a dynamical instability when the solar system was about 600 million years old, resulting in giant planets and smaller bodies to be scattered away from each other.

Some small bodies moved into the Kuiper Belt and others traveled inward, which produced impacts on the terrestrial planets and the Moon.

Jupiter scattered most small bodies outward and moved inward, but Nesvorny said this planet presents a problem.

Slow changes in Jupiter's orbit would have conveyed too much momentum to the orbits of the terrestrial planets, stirring up or disrupting the inner solar system and possibly caused the Earth to collide with Mars or Venus.

"Colleagues suggested a clever way around this problem," Nesvorny said in a press release. "They proposed that Jupiter's orbit quickly changed when Jupiter scattered off of Uranus or Neptune during the dynamical instability in the outer solar system."

The "jumping-Jupiter" theory is less harmful to the inner solar system, because the orbital coupling between the terrestrial planets and Jupiter is weak if Jupiter jumps.

Nesvorny detected Jupiter did jump by scattering from Uranus or Neptune. However, he said when it jumped, Uranus or Neptune was knocked out of the solar system.

He then had to create a simulation with an additional giant planet with mass similar to Uranus or Neptune to determine what really happened 600 million years ago.

He found that another giant planet was ejected from the solar system by Jupiter, leaving four giant planets behind and the terrestrial planets undisturbed.

"The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence," Nesvorny said in a press release.

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Image Caption: Artist's impression of a planet ejected from the early solar system. Image courtesy of Southwest Research Institute